The invention relates to a machine for assisting the spontaneous respiration of a patient, having a respiratory-gas mixing unit for mixing air and oxygen in a desired ratio in order to supply the patient with respiratory gas of an adjustable oxygen concentration, an outlet on which are disposed a pressure regulator, a gas duct connecting the respiratory-gas mixing unit to the outlet, and a patient line which branches off from the gas duct on a junction arranged between the respiratory-gas mixing unit and the outlet.
Patients who breathe spontaneously usually need no mechanical respiration. Nevertheless, it is frequently necessary, particularly within the purview of intensive care, to assist their respiration. This is done, for example, by raising the oxygen concentration relative to the normal oxygen content of the air and by a slight elevation of the pressure (by 3 to 15 mbar) in comparison with the normal air pressure.
To help the patient to get used to normal respiration, it is advisable to provide him continuously with respiratory gas having a largely constant pressure. Machines that assist the respiration of spontaneously breathing patients in this way are called "CPAP" (continuous positive airway pressure) machines.
Modern respirators frequently have the option of establishing a CPAP function. With these respirators, however, an adjustable trigger level must usually be exceeded to initiate the inspiration phase, and this can stress the patient. Moreover, respirators have a very complex technical design and are therefore expensive. Thus, their use for the CPAP function is uneconomical.
For these reasons, special machines of the type mentioned in the introduction have been developed. The respiratory gas is taken from the central air and oxygen supply systems normally present in the clinics and are mixed by means of mechanical respiratory-gas mixing units (so-called "oxyblenders"). A water lock is normally used as a pressure regulator at the outlet of the gas duct, whereby the immersion depth of the outflow orifice determines the level of the pressure. To damp the pressure fluctuations caused by the respiratory activity of the patient, large-volume, elastic accumulators are used.
In order to ensure the necessary constant respiratory-gas composition, a high degree of technical complexity must designed into the machines of known construction. Nevertheless, uncertainties exist. Therefore, the machines must be monitored constantly by a qualified staff, or complex additional monitoring and alarm devices must be provided. Accordingly, the object of the invention is to provide a spontaneous-respiration-assisting machine which is improved in these respects and which can nevertheless be made inexpensively.